1. Field of the Invention
This invention relates to a process for the conversion of aldehydes to esters, specifically acrolein or methacrolein to methyl acrylate or methyl methacrylate, respectively. In the process, an aldehyde is contacted with an oxidizing agent to form an intermediate and then the intermediate is contacted with a diol or an alcohol to form an ester. Specifically, acrolein or methacrolein is contacted with an oxidizing agent which is also a chlorinating agent, such as t-butyl hypochlorite, and the chlorinated compound is contacted with an alcohol, such as methanol, to form methyl acrylate or methyl methacrylate, respectively.
2. Description of the Prior Art
Manufacture of methyl acrylate (MA) and methyl methacrylate (MMA) can be accomplished by progressive oxidation of propylene to acrolein and to acrylic acid and esterification to methyl acrylate and of isobutylene to methacrolein and methacrylic acid and to methyl methacrylate, respectively. The first oxidation is a catalytic reaction that converts an olefin in the presence of oxygen to an unsaturated aldehyde and water:
H2Cxe2x95x90CAx-CH3+O2xe2x86x92H2Cxe2x95x90CAx-CHO+H2O 
where A is hydrogen or an alkyl group.
The catalyst is generally a multi-component mixed metal oxide catalyst, typically molybdenum based.
The second oxidation is also a catalytic reaction that converts an unsaturated aldehyde in the presence of oxygen to an unsaturated carboxylic acid:
H2Cxe2x95x90CAx-CHO+xc2xdO2xe2x86x92H2Cxe2x95x90CAx-COOH 
The catalyst is generally a multi-component mixed metal oxide or heteropoly compound catalyst, also typically molybdenum based.
Esterification of the unsaturated carboxylic acid is also a catalytic reaction that converts the unsaturated carboxylic acid in the presence of an alcohol to an unsaturated ester:
H2Cxe2x95x90CAx-COOH+Axe2x80x2OHxe2x86x92H2Cxe2x95x90CAx-COOAxe2x80x2+H2O 
where Axe2x80x2 is an alkyl group.
An article entitled xe2x80x9cA Novel, Nonoxidative Method for the Conversion of Aldehydes to Estersxe2x80x9d by Stephen R. Wilson et al published in J. Org. Chem., vol. 47, pages 1360-1 (1982), disclosed conversion of (cyclobutadiene)iron tricarbonyl to tricarbonyl (methyl 1-4-v-1,3-cyclobutadiene-carboxylate)iron or tricarbonyl (isophorol 1-4-v-1,3-cyclobutadiene-carboxylate)iron with tert-butyl hypochlorite and methanol or isophorol, respectively, and conversion of cinnamaldehyde to methylcinnamate with tert-butyl hypochlorite and methanol. The choice of solvent appeared to control the product obtained. For example, it was reported that the reaction of tert-butyl hypochlorite with cinnamaldehyde in methanol produced 2-chloro-3-methoxy-3-phenylpropanal whereas the reaction of tert-butyl hypochlorite with cinnamaldehyde in carbon tetrachloride produced 1-chloro-3-phenylpropanal. There was no disclosure of the effectiveness of chlorinating aliphatic aldehydes for conversion to esters or of the effect of solvents on such a process.
Hypochlorites have been used in other chemical reactions. U.S. Pat. No. 3,488,394 discloses the hydroxylation of olefins by reacting olefin and a hypochlorite in the presence of OsO4 while U.S. Pat. No. 3,846,478 discloses the reaction of a hypochlorite and olefin in an aqueous medium and in the presence of OsO4 catalyst to hydroxylate the olefin. Both of these procedures can employ co-solvents such as t-butyl alcohol. When this is done, it is disclosed that there is some tendency for allylic chlorination of the olefinic compound to occur, e.g., by the action of t-butyl hypochlorite formed from reaction of the t-butyl alcohol and sodium hypochlorite (NaOCl). Alternatively, part of the t-butyl hypochlorite can react with allyl alcohol to form a chlorinated ether.
U.S. Pat. No. 6,127,556 discloses t-butyl hypochlorite as an oxidizing agent in a multi-step conversion of aldehydes to epoxides.
U.S. Pat. No. 4,110,533 discloses t-butyl hypochlorite in a process for the manufacture of enol derivatives and the conversion of a thio grouping into a sulfoxide grouping by oxidation of a 2-cephem compound to the corresponding oxide in the presence of an inert solvent, such as a halogenated hydrocarbon like methylene chloride.
U.S. Pat. No. 4,007,211 discloses t-butyl hypochlorite in process to convert an alpha-thio carboxylic acid to the corresponding ketone by removing the carboxylic carbon by oxidative decarboxylation.
The conversion of aldehyde to ester without the presence of a metal catalyst would be advantageous. Oxidation of the metal sites can result in poor catalyst performance.
Accordingly, an object of this invention is to provide a process for converting aldehydes to esters with an oxidizing agent and a diol or an alcohol.
And, an object of this invention is to provide an oxidizing agent, preferably one which is also a chlorinating agent, to form an intermediate of an acyl chloride from an aldehyde.
Also, an object of this invention is to provide an anhydrous process for converting aldehydes to esters.
Further, an object of this invention is to provide a process in the absence of solvents for converting aldehydes to esters.
Additionally, an object of this invention is to provide a process for converting aldehydes to esters in a single batch reactor.
These and other objects are accomplished by a process for producing esters from aldehydes with an oxidizing agent, preferably one which is also a chlorinating agent, and a diol or an alcohol.
This invention relates to a process for producing esters from aldehydes comprising reacting essentially in the absence of water an aldehyde having the general formula of RCHO, wherein R is an alkenyl group or alkyl group having one to six carbon atoms, with an oxidizing agent having the general formula Rxe2x80x23COX, wherein Rxe2x80x2 is an alkyl group having one to six carbon atoms bonded to a tertiary carbon atom, each Rxe2x80x2 being the same or different, and wherein X is a halogen, to form an intermediate and reacting the intermediate with an alcohol having the general formula of Rxe2x80x3OH or a diol having the general formula HORxe2x80x2xe2x80x3OH, wherein Rxe2x80x3 is an alkyl group or alkoxy group having one to eight carbon atoms or an aryl group having six to ten carbon atoms and Rxe2x80x2xe2x80x3 is an alkyl group having one to eight carbon atoms or an aryl group having six to ten carbon atoms to form an ester having the general formula RCOORxe2x80x3 or RCOORxe2x80x2xe2x80x3OH or a diester having the general formula RCOORxe2x80x2xe2x80x3OOCR.
This invention also relates to a process for producing an ester from an aldehyde comprising (a) contacting an aldehyde having the general formula of RCHO, wherein R is an ethenyl or isopropenyl group, with an oxidizing agent having the general formula Rxe2x80x23COX, wherein Rxe2x80x2 is an alkyl group having one to six carbon atoms bonded to a tertiary carbon atom, each Rxe2x80x2 being the same or different, and wherein X is a halogen, to form an intermediate; and (b) contacting an alcohol having the general formula of Rxe2x80x3OH or a diol having the general formula HORxe2x80x2xe2x80x3OH, wherein Rxe2x80x3 is an alkyl group or alkoxy group having one to eight carbon atoms or an aryl group having six to ten carbon atoms and Rxe2x80x2xe2x80x3 is an alkyl group having one to eight carbon atoms or an aryl group having six to ten carbon atoms, with the intermediate to form an ester having the general formula RCOORxe2x80x3 or RCOORxe2x80x2xe2x80x3OH or a diester having the general formula RCOORxe2x80x2xe2x80x3OOCR wherein the process is carried out essentially in the absence of water.
The reaction sequence of the present invention is as follows: 
This invention is generally a process for converting aldehydes to esters by contacting the aldehyde with an oxidizing agent and then with a diol or an alcohol. The oxidizing agent is preferably also a chlorinating agent such as t-butyl hypochlorite.
To achieve the objects of the present invention, the reaction between the aldehyde and the oxidizing/chlorinating agent should favor free-radical abstraction of hydrogen and replacement with a halogen in the aldehyde group. Subsequently contacting the halogenated intermediate with a diol or an alcohol produces an ester by replacing the halogen with an alkoxy group from the diol or alcohol.
An aldehyde of the general formula of RCHO, R being an alkenyl group or an alkyl group having one to six carbon atoms would be effective in the present invention. Preferably, the aldehyde is acrolein or methacrolein.
An oxidizing agent of the general formula Rxe2x80x23COX wherein Rxe2x80x2 is an alkyl group having one to six carbon atom bonded to a tertiary carbon atom and X is a halogen would be effective in the present invention. Preferably, Rxe2x80x2 is a methyl, an ethyl or a propyl group.
Each Rxe2x80x2 may be the same or different, but preferably all Rxe2x80x2 are the same. X may be fluorine, chlorine, bromine or iodine but preferably is chlorine. Most preferably, the oxidizing agent is also a chlorinating agent, such as t-butyl hypochlorite.
An alcohol of the general formula of Rxe2x80x3OH wherein Rxe2x80x3 is an alkyl group or an alkoxy group having one to eight carbon atoms or is an aryl group having six to ten carbon atoms would be effective in the present invention. Preferably, the alcohol is methanol, n-butanol, t-butanol, allyl alcohol, 2-ethylhexanol, cyclohexanol, phenol, glycidol, 2-ethoxyethanol or 2-hydroxy ethanol. Most preferably, the alcohol is methanol. A diol of the general formula of HORxe2x80x2xe2x80x3OH wherein Rxe2x80x2xe2x80x3 is an alkyl group having one to eight carbon atoms or is an aryl group having six to ten carbon atoms would be effective in the present invention. Preferably, the diol is 1,4-butanediol or ethylene glycol.
An ester of the general formula RCOORxe2x80x3 or RCOORxe2x80x2xe2x80x3OH or a diester of the general formula RCOORxe2x80x2xe2x80x3OOCR wherein R, Rxe2x80x3 and Rxe2x80x2xe2x80x3 are as defined above could be produced by the process of the present invention. Preferably, if aldehyde is acrolein, the ester is methyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, glycidyl acrylate, phenyl acrylate, 2-ethoxyethyl acrylate, 1,4-butanediol monoacrylate, 1,4-butanediol diacrylate, 2-hydroxy monoacrylate or ethylene glycol diacrylate and, if the aldehyde is methacrolein, the ester is methyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, allyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate or glycidyl methacrylate. Most preferably, the ester is methyl acrylate or methyl methacrylate.
Generally, the aldehyde is contacted with the oxidizing agent while stirring. If the aldehyde is acrolein or methacrolein and the oxidizing agent is t-butyl hypochlorite, the reaction is exothermic. The temperature of the reaction mixture should be maintained in the range from xe2x88x9215 to 75xc2x0 C., preferably from xe2x88x925 to 25xc2x0 C. and most preferably about 25xc2x0 C. The reaction temperature between acrolein or methacrolein and t-butyl hypochlorite typically would be 15xc2x0 C.(xc2x1)10xc2x0C. The molar ratio of t-butyl hypochlorite to acrolein or methacrolein is in the range of 1:0.8 to 1:3, but preferably there is a stoichiometric excess of acrolein or methacrolein. The preferred molar ratio of t-butyl hypochlorite to acrolein or methacrolein is in the range of 1:1.3 to 1:2. Contact time between the acrolein or methacrolein and t-butyl hypochlorite will vary with the amount of reactants but the reaction between acrolein or methacrolein and t-butylhypochlorite should continue until the excess t-butyl hypochlorite or excess acrolein or methacrolein is no longer detectable by gas chromatography or other means of chemical analysis.
Generally, the chlorinated intermediate formed from the aldehyde is contacted with the diol or alcohol, preferably while stirring. If the aldehyde is acrolein or methacrolein and the desired ester is methyl acrylate or methyl methacrylate, the alcohol is methanol. The temperature of the solution when the diol or the alcohol is added is in the range of from 15 to 75xc2x0 C., more preferably about 25xc2x0 C. Preferably, the molar ratio of t-butyl hypochlorite:methanol is in the range from 1:2 to 1:25, more preferably in the range from 1:2.25 to 1:17. When the diol or alcohol is contacted with the chlorinated intermediate, hydrogen chloride is formed. Contact time between the chlorinated intermediate and the diol or alcohol will vary with the amount of reactants but the reaction should continue until the presence of the chlorinated intermediate is no longer detectable by gas chromatography or other means of chemical analysis.
Hydrogen chloride is a byproduct of the reaction. The presence of hydrogen chloride may affect the formation of the desired product or cause an unfavorable pH environment. A base may be added before, during or after the addition of the diol or alcohol to neutralize the hydrogen chloride. Preferably, the base is added prior to or concurrently with the addition of the diol or alcohol. The base can be an organic amine, such as pyridine, triethylamine or morpholine, or an inorganic base, such as sodium carbonate or sodium bicarbonate. The base most preferred is sodium bicarbonate. The base is present in the range from 0.5 to 1.5 equivalents relative to t-butyl hypochlorite, preferably in the range from 0.8 to 1.1 equivalents, most preferably about 0.9 equivalents when the diol or alcohol is present in the range from 1.5 to 8.5 equivalents relative to t-butyl hypochlorite, preferably in the range from 2.0 to 5.2 equivalents, most preferably 2.25 equivalents.
The process of the present invention must be carried out in anhydrous conditions, i.e., essentially in the absence of water. The presence of water results in the formation of by-products instead of the desired esters, e.g., acrylic acid or methacrylic acid instead of methyl acrylate or methyl methacrylate.
The process of the present invention can be carried out in the absence or in the presence of solvent. Preferably, solvent is not present. If a solvent is present it should be inert to chlorine. Preferably, the solvent is carbon tetrachloride, chlorobenzene, chloroform, methylene chloride (dichloromethane), tetrachloroethylene or t-butanol and, most preferably, is carbon tetrachloride.
The invention having been generally described, the following examples are given as particular embodiments of the invention and to demonstrate the practice and advantages thereof. It is understood that the examples are given by way of illustration and are not intended to limit the specification or the claims to follow in any manner.